China’s regional social vulnerability to geological disasters: evaluation and spatial characteristics analysis

The Andaman–Sumatra is one of the seismically active subduction zones and experienced three largest earthquakes in the recent past and rupturing more than 1,600-km-long portion of the plate boundary. The seismicity analysis of these large earthquakes source region (5°S–15°N latitude and 90°E–103°E longitude) has been carried out by several researchers and quantified the spatial and temporal variation of b-value which is a proxy to differential stress conditions and fractal dimension which is an indicator of material heterogeneity and strength. The results of all these studies clearly bring out the low b-value and low fractal dimension corresponding to locales were sizable magnitude earthquakes have occurred. Further locales of high stress regions are identified.     

Transtensional deformation in the Lake Tahoe region, California and Nevada, USA

Dextral transtensional deformation is occurring along the Sierra Nevada–Great Basin boundary zone (SNGBBZ) at the eastern edge of the Sierra Nevada microplate. In the Lake Tahoe region of the SNGBBZ, transtension is partitioned spatially and temporally into domains of north–south striking normal faults and transitional domains with conjugate strike-slip faults. The normal fault domains, which have had large Holocene earthquakes but account only for background seismicity in the historic period, primarily accommodate east–west extension, while the transitional domains, which have had moderate Holocene and historic earthquakes and are currently seismically active, primarily record north–south shortening. Through partitioned slip, the upper crust in this region undergoes overall constrictional strain.Major fault zones within the Lake Tahoe basin include two normal fault zones: the northwest-trending Tahoe–Sierra frontal fault zone (TSFFZ) and the north-trending West Tahoe–Dollar Point fault zone. Most faults in these zones show eastside down displacements. Both of these fault zones show evidence of Holocene earthquakes but are relatively quiet seismically through the historic record. The northeast-trending North Tahoe–Incline Village fault zone is a major normal to sinistral-oblique fault zone. This fault zone shows evidence for large Holocene earthquakes and based on the historic record is seismically active at the microearthquake level. The zone forms the boundary between the Lake Tahoe normal fault domain to the south and the Truckee transition zone to the north.Several lines of evidence, including both geology and historic seismicity, indicate that the seismically active Truckee and Gardnerville transition zones, north and southeast of Lake Tahoe basin, respectively, are undergoing north–south shortening. In addition, the central Carson Range, a major north-trending range block between two large normal fault zones, shows internal fault patterns that suggest the range is undergoing north–south shortening in addition to east–west extension.A model capable of explaining the spatial and temporal partitioning of slip suggests that seismic behavior in the region alternates between two modes, one mode characterized by an east–west minimum principal stress and a north–south maximum principal stress as at present. In this mode, seismicity and small-scale faulting reflecting north–south shortening concentrate in mechanically weak transition zones with primarily strike-slip faulting in relatively small-magnitude events, and domains with major normal faults are relatively quiet. A second mode occurs after sufficient north–south shortening reduces the north–south S_hmax in magnitude until it is less than S_v, at which point S_v becomes the maximum principal stress. This second mode is then characterized by large earthquakes on major normal faults in the large normal fault domains, which dominate the overall moment release in the region, producing significant east–west extension.     

Seismogenesis of clustered seismicity beneath the Kangra–Chamba sector of northwest Himalaya: Constraints from 3D local earthquake tomography

To investigate subsurface structure and seismogenic layers, 3D velocity inversion was carried out in the source zone of 1905 Kangra earthquake (M8.0) in the northwestern Himalaya. P-wave and S-wave phase data of 159 earthquakes recorded by a network of 21 stations were used for this purpose. Inverted velocity tomograms up to a depth range of 18 km show significant variations of 14% in Vp and Vs and 6% in the Vp/Vs across the major tectonic zones in the region. Synthesis of seismicity pattern, velocity structure, distinctive focal mechanisms coupled with nature of stress distribution allows mapping of three different source regions that control regional seismotectonics. Accumulating strains are partly consumed by sliding of Chamba Nappe to the southwest through reverse-fault movements along Chamba/Panjal/Main Boundary Thrusts. This coupled with normal-fault type displacements along Chenab Normal Fault in the north account for low magnitude widespread seismicity in upper 8–10 km of the crust. At intermediate depths from 8 to 15 km, adjusting to residual compressive stresses, the detachment or lower end of the MBT slips to produce thrust dominated seismicity. Nucleation of secondary stresses in local NE–SW oriented structure interacts in complex manner with regional stresses to generate normal type earthquakes below the plane of detachment and therefore three seismic regimes at different depths produce intense seismicity in a block of 30 × 30 km² centered NE to the epicenter of Kangra earthquake.     

Seismicity and velocity structures along the south-Alpine thrust front of the Venetian Alps (NE-Italy)

In this paper we show the seismicity and velocity structure of a segment of the Alpine retro-belt front along the continental collision margin of the Venetian Alps (NE Italy). Our goal is to gain insight on the buried structures and deep fault geometry in a “silent” area, i.e., an area with poor instrumental seismicity but high potential for future earthquakes, as indicated by historical earthquakes (1695 Me = 6.7 Asolo and 1936 Ms = 5.8 Bosco del Cansiglio). Local earthquakes recorded by a dense temporary seismic network are used to compute 3-D Vp and Vp/Vs tomographic images, yielding well resolved images of the upper crust underneath the south-Alpine front. We show the presence of two main distinct high Vp S-verging thrust units, the innermost coincides with the piedmont hill and the outermost is buried under a thick pile of sediments in the Po plain.Background seismicity and Vp/Vs anomalies, interpreted as cracked fluid-filled volumes, suggest that the NE portion of the outermost blind thrust and its oblique/lateral ramps may be a zone of high fluid pressure prone to future earthquakes.Three-dimensional focal mechanisms show compressive and transpressive solutions, in agreement with the tectonic setting, stress field maps and geodetic observations. The bulk of the microseismicity is clustered in two different areas, both in correspondence of inherited lateral ramps of the thrust system. Tomographic images highlight the influence of the paleogeographic setting in the tectonic style and seismic activity of the region.     

The origin of large or great thrust-type earthquakes along subducting plate boundaries

Seismicity, deformation, state of stress, and abundance of fluids along subducting plate boundaries are reviewed, and the origin of large or great thrust-type earthquakes is discussed based on the recent experimental results on the slip behavior of halite and serpentine gouges.Shallow subducting plate boundaries above 20–25 km in depth are characterized by low seismicity, low tectonic stress, inter-plate decoupling, ductile deformation associated with the formation of metamorphic schistosity (except at very shallow depths), metamorphism suggesting solution processes on massive scale, and presence of abundant H₂O. It is argued that these unique features are due to pressure-solution processes, to high fluid pressure, to low strength and stable behavior of clayey sediments under wet environments, and/or to the deformation of soft, unconsolidated sediments at very shallow depths. The low seismicity in this zone is in marked contrast with major strike-slip faults along which large earthquakes occur at depths shallower than 15–20 km. It is emphasized that these unique features are expected only for restricted regions where there is constant supply of H₂O due to progressive metamorphism or where fluids in the rocks are trapped and cannot escape to the surface.Large or great thrust-type earthquakes in subduction zones initiate at depths of 30–50 km, below the shallow decoupled zone. In this focal depth range, the supply of H₂O during progressive metamorphism perhaps diminishes downwards, the overriding and subducting plates are coupled and stick to each other during much of the inter-seismic period, and the resistance to slip (or shear stress) is presumably high. It is suggested that these earthquakes begin to occur at a depth where the plate-boundary zone becomes fairly dry. Deformation at these depths appears to be predominantly ductile, so that the earthquakes cannot be regarded simply as a brittle phenomenon. (1) Creep instability i.e., instability associated with plastic deformation, and (2) dehydration-induced instability are the most likely mechanisms for initiating the earthquakes, and both have some experimental support. Stick-slip of halite gouge while undergoing ductile deformation primarily by intracrystalline gliding is described and discussed as a supporting evidence for (1). Shear resistance of halite gouge increases with increasing confining pressure in stick-slip regimes. Hence the observed stick-slip may be a semi-brittle phenomenon with respect to the pressure dependence of the shear resistance, although the deformation texture cannot be distinguished from that formed by pressure-insensitive flow. Serpentine gouge exhibits violent stick-slip upon its decomposition under dry, not wet, environments, supporting the mechanism (2) above. Exact mechanisms which lead to the unstable fault motion are poorly understood as yet, but stick-slip of both halite and serpentine gouges is recognized only when the slip-rate dependence of friction is negative i.e., lower friction at faster slip rate, consistent with the theoretical prediction of Rice and Ruina (1983). There is a possibility that the thrust-type earthquakes can be explained essentially within the framework of fault constitutive laws developed by Dieterich (1979) and Ruina (1983).     

Relation between electrical resistivity and earthquake generation in the crust of West Anatolia, Turkey

In this paper, we present a relation between the earthquake occurrence and electric resistivity structures in the crust, in West Anatolia and the Thrace region of Turkey. The relationship between magnetotelluric georesistivity models and crustal earthquakes in West Anatolia, during a period from 1900 to 2000, is investigated. It is found that most of the large crustal earthquakes occurred in and around the areas of the highest electrical resistivity in the upper crust, although rare small magnitude earthquakes are observed in some parts of the conductive lower crust in West Anatolian extensional terrain. The high-resistivity zones may represent rocks that are probably mechanically strong enough to permit sufficient stress to accumulate for earthquakes to occur in western Anatolia and the Thrace region. However, some recent studies state that the generation of a large earthquake is not only a pure mechanical process, but is closely related to fluid existence. We also reviewed recent world-wide researches including results from the Anatolian data for the first time and discussed all general findings in combination. Our findings show that the boundary between the resistive upper crust and the conductive lower crust correlates well with the cutout depth of the seismicity in West Anatolia and Thrace. This boundary is also attributed to the fluid bearing brittle–ductile transition zone in world literature. Fluid migration from the conductive lower crust to the resistive upper crust may contribute the seismicity in resistive zones. Alternatively, the upper–lower crust boundary may act as a stress concentrator and fluids may help to release strain energy in brittle parts of lower crust, by small magnitude earthquakes, whereas they may help in focusing strain in mechanically strong and electrically resistive zones for large earthquakes to occur.     

Assessment of flexural analysis applied to the Sumatra-Java subduction zone

Indian Ocean subduction zone is one of the most active plate margins of the globe as evident from its vast record of great magnitude earthquake and tsunami events. We use Bouguer admittance (Morlet isostatic response function) in Sumatra-Java subduction zones comprising both the subduction and over-riding plates to determine the lithospheric mechanical strength variations. We determine effective elastic thickness (T _e ) for five oceanic windows (size 990 × 990 km²) by analyzing the admittance using Bouguer gravity and bathymetry data. The results show bimodal T _e values < 20 km for Sumatra and 20−40 km for Java. The lower bimodal values obtained for Sumatra appears to correlate well with the zones of historical seismicity. This is in sharp contrast with Java subduction zone, which shows higher T _e values (20–40 km) and apparently associated with low magnitude earthquakes. We suggest a strong and wide interseismic coupling for Sumatra between the subducting and over-riding plates, and deeper mantle contributing to low strength, shallow focus — high magnitude seismicity and vice versa for Java, leading to their seismogenic zonation.     

Characteristics of ring seismicity in different depth ranges before large and great earthquakes in the Sumatra region

Characteristics of the seismicity in depth ranges 0–33 and 34–70 km before ten large and great (M _w = 7.0−9.0) earthquakes of 2000–2008 in the Sumatra region are studied, as are those in the seismic gap zones where no large earthquakes have occurred since at least 1935. Ring seismicity structures are revealed in both depth ranges. It is shown that the epicenters of the main seismic events lie, as a rule, close to regions of overlap or in close proximity to “shallow” and “deep” rings. Correlation dependences of ring sizes and threshold earthquakes magnitudes on energy of the main seismic event in the ring seismicity regions are obtained. Identification of ring structures in the seismic gap zones (in the regions of Central and South Sumatra) suggests active processes of large earthquake preparation proceed in the region. The probable magnitudes of imminent seismic events are estimated from the data on the seismicity ring sizes.     

Influence of slow active faults in probabilistic seismic hazard assessment: the northwestern margin of the València trough

Areas of low strain rate are typically characterized by low to moderate seismicity. The earthquake catalogs for these regions do not usually include large earthquakes because of their long recurrence periods. In cases where the recurrence period of large earthquakes is much longer than the catalog time span, probabilistic seismic hazard is underestimated. The information provided by geological and paleo-seismological studies can potentially improve seismic hazard estimation through renewal models, which assume characteristic earthquakes. In this work, we compare the differences produced when active faults in the northwestern margin of the València trough are introduced in hazard analysis. The differences between the models demonstrate that the introduction of faults in zones characterized by low seismic activity can give rise to significant changes in the hazard values and location. The earthquake and fault seismic parameters (recurrence interval, segmentation or fault length that controls the maximum magnitude earthquake and time elapsed since the last event or T_e) were studied to ascertain their effect on the final hazard results. The most critical parameter is the recurrence interval, where shorter recurrences produce higher hazard values. The next most important parameter is the fault segmentation. Higher hazard values are obtained when the fault has segments capable of producing big earthquakes. Finally, the least critical parameter is the time elapsed since the last event (T_e), when longer T_e produces higher hazard values.     

Time independent seismic hazard analysis in Alborz and surrounding area

The Bayesian probability estimation seems to have efficiencies that make it suitable for calculating different parameters of seismicity. Generally this method is able to combine prior information on seismicity while at the same time including statistical uncertainty associated with the estimation of the parameters used to quantify seismicity, in addition to the probabilistic uncertainties associated with the inherent randomness of earthquake occurrence. In this article a time-independent Bayesian approach, which yields the probability that a certain cut-off magnitude will be exceeded at certain time intervals is examined for the region of Alborz, Iran, in order to consider the following consequences for the city of Tehran. This area is located within the Alpine-Himalayan active mountain belt. Many active faults affect the Alborz, most of which are parallel to the range and accommodate the present day oblique convergence across it. Tehran, the capital of Iran, with millions of inhabitants is located near the foothills of the southern Central Alborz. This region has been affected several times by historical and recent earthquakes that confirm the importance of seismic hazard assessment through it. As the first step in this study an updated earthquake catalog is compiled for the Alborz. Then, by assuming a Poisson distribution for the number of earthquakes which occur at a certain time interval, the probabilistic earthquake occurrence is computed by the Bayesian approach. The highest probabilities are found for zone AA and the lowest probabilities for zones KD and CA, meanwhile the overall probability is high.     

A seismotectonic study of the Southeastern Alaska Region

We compare relocations of recent (1973–2005) and historic (1919–1972) earthquakes to geologic and geophysical (gravity, aeromagnetic, and uplift) information to determine the relationship of seismicity to crustal deformation in southeastern Alaska. Our results suggest that along strike changes in the structure of the Pacific plate may control the location of the ends of rupture zones for large earthquakes along the offshore Queen Charlotte fault system in the southern portion of the study area. There is a marked increase in background seismicity in the northern portion of the study area where the Fairweather fault begins to bend toward the northwest and crustal uplift due to glacial unloading exceeds 20 mm/year. Focal mechanisms indicate that thrust and reverse mechanisms predominate in the region of maximum uplift, as might be expected by the decrease in ice sheet thickness. The diffuse nature of seismicity between the Fairweather and Denali faults in the northern study area suggests a complex interaction between plate/microplate interactions and glacial unloading, making it difficult to determine the optimal fault orientation for failure in moderate magnitude (5.5 to 6.5) earthquakes within this region.     

江苏—南黄海地区地震活动时空分布特征及其孕震构造分析

江苏—南黄海地区城市密集,人口众多,是中国东部经济最发达的地带之一。同时,该地区历史上曾频发中—强以上级别的地震,地震及次生地质灾害是威胁该区经济社会发展的自然灾害之一。该区的地震活动时空特征和发震机制还不清楚。本文通过整理江苏—南黄海地区的历史和仪器记录地震数据,分析了该区地震活动时空分布格局,发现地震活动主要集中于若干条区域活动断裂带,在时间上具有约60年的平静期,目前仍处于地震活跃期。深部构造研究还表明该区域内地震活跃的南部坳陷和勿南沙隆起区均存在显著的地球物理异常,表明地震活动与区域深部构造有关。东部菲律宾海板块的俯冲作用和印度—欧亚大陆碰撞引起的板块边界挤压力和大陆边缘因地形高程差异伴随的重力势能是中国海洋地震的主要驱动力。上述认识不仅加深了对江苏—南黄海地区地震构造环境的理解,同时也能对该区防震减灾公益事业提供科学参考。     

Forecasting rupture dimension using the pattern informatics technique

The Pattern Informatics (PI) technique [Tiampo, K.F., Rundle, J.B., McGinnis, S., Gross, S., Klein, W., 2002. Mean-field threshold systems and phase dynamics: An application to earthquake fault systems, Europhys. Lett., 60, 481–487] is founded on the premise that changes in the seismicity rate are a proxy for changes in the underlying stress. This new approach to the study of seismicity quantifies its local and regional space–time patterns and identifies regions of local quiescence or activation. Here we use a modification of the PI method to quantify localized changes surrounding the epicenters of large earthquakes in California in an attempt to objectively quantify the rupture zones of these upcoming events. We show that this method can be used to forecast the size and magnitude of future earthquakes.     

Structural characteristics off Miyagi forearc region, the Japan Trench seismogenic zone, deduced from a wide-angle reflection and refraction study

The Japan Trench subduction zone, located east of NE Japan, has regional variation in seismicity. Many large earthquakes occurred in the northern part of Japan Trench, but few in the southern part. Off Miyagi region is in the middle of the Japan Trench, where the large earthquakes (M > 7) with thrust mechanisms have occurred at an interval of about 40 years in two parts: inner trench slope and near land. A seismic experiment using 36 ocean bottom seismographs (OBS) and a 12,000 cu. in. airgun array was conducted to determine a detailed, 2D velocity structure in the forearc region off Miyagi. The depth to the Moho is 21 km, at 115 km from the trench axis, and becomes progressively deeper landward. The P-wave velocity of the mantle wedge is 7.9–8.1 km/s, which is typical velocity for uppermost mantle without large serpentinization. The dip angle of oceanic crust is increased from 5–6° near the trench axis to 23° 150 km landward from the trench axis. The P-wave velocity of the oceanic uppermost mantle is as small as 7.7 km/s. This low-velocity oceanic mantle seems to be caused by not a lateral anisotropy but some subduction process. By comparison with the seismicity off Miyagi, the subduction zone can be divided into four parts: 1) Seaward of the trench axis, the seismicity is low and normal fault-type earthquakes occur associated with the destruction of oceanic lithosphere. 2) Beneath the deformed zone landward of the trench axis, the plate boundary is characterized as a stable sliding fault plain. In case of earthquakes, this zone may be tsunamigenic. 3) Below forearc crust where P-wave velocity is almost 6 km/s and larger: this zone is the seismogenic zone below inner trench slope, which is a plate boundary between the forearc and oceanic crusts. 4) Below mantle wedge: the rupture zones of thrust large earthquakes near land (e.g. 1978 off Miyagi earthquake) are located beneath the mantle wedge. The depth of the rupture zones is 30–50 km below sea level. From the comparison, the rupture zones of large earthquakes off Miyagi are limited in two parts: plate boundary between the forearc and oceanic crusts and below mantle wedge. This limitation is a rare case for subduction zone. Although the seismogenic process beneath the mantle wedge is not fully clarified, our observation suggests the two possibilities: earthquake generation at the plate boundary overridden by the mantle wedge without serpentinization or that in the subducting slab.     

Earthquake Hazard in Italy, 2001–2030

The study computes time-dependant earthquake probabilities on the basis of seismicity data mainly deriving from historic records. It provides a methodological approach useful for those countries where the scarcity of instrumental data and/or paleoseismological evidences requires that historical information shall be stressed. Thus, the conditional probability that damaging earthquakes (M ≥ 6) may occur in Italy in the next 30 years is shown, and the potential for the main worldwide known Italian cities with a cultural heritage is outlined. Earthquake probabilities are computed referring to the application of renewal processes, where the periodicity is analytically modelled by means of the Brownian Passage Time function; an estimate of the dispersion (i.e., uncertainty) introduced on probabilities is provided making use of Monte Carlo simulations. The computed probabilities refer to seismic source zones deriving from the spatial clustering of the historically documented seismicity. The computation of probabilities based on the interaction of earthquakes occurring in nearby zones, has been also attempted for a test area to explore the influence exerted by the stress transfer effect. The main findings of this study are that (1) seismic source zones in Southern Italy are the most prone to experience damaging earthquakes in the next 30-years, with conditional probabilities a large as 10%; and (2) the influence exerted by the earthquake interaction in increasing such probabilities, doesn’t seem to be relevant, because the mean recurrence times of large earthquakes (above the threshold magnitude of six chosen in this study) are in general much longer than the time shortening produced by the stress transfer.     

Seismicity of Gujarat

Paper describes tectonics, earthquake monitoring, past and present seismicity, catalogue of earthquakes and estimated return periods of large earthquakes in Gujarat state, western India. The Gujarat region has three failed Mesozoic rifts of Kachchh, Cambay, and Narmada, with several active faults. Kachchh district of Gujarat is the only region outside Himalaya-Andaman belt that has high seismic hazard of magnitude 8 corresponding to zone V in the seismic zoning map of India. The other parts of Gujarat have seismic hazard of magnitude 6 or less. Kachchh region is considered seismically one of the most active intraplate regions of the World. It is known to have low seismicity but high hazard in view of occurrence of fewer smaller earthquakes of M????6 in a region having three devastating earthquakes that occurred during 1819 (M _w7.8), 1956 (M _w6.0) and 2001 (M _w7.7). The second in order of seismic status is Narmada rift zone that experienced a severely damaging 1970 Bharuch earthquake of M5.4 at its western end and M????6 earthquakes further east in 1927 (Son earthquake), 1938 (Satpura earthquake) and 1997 (Jabalpur earthquake). The Saurashtra Peninsula south of Kachchh has experienced seismicity of magnitude less than 6.     

Potential source zones for Himalayan earthquakes: constraints from spatial�Ctemporal clusters

The Himalayan fold-thrust belt has been visited by many disastrous earthquakes (magnitude > 6) time and again. This active collisional orogen bordering Indian subcontinent in the north remains a potential seismic threat of similar magnitude in the adjoining countries like India, Pakistan, Nepal, Bhutan and China. Though earthquake forecasting is riddled with all conjectures and still not a proven presumption, identifying likely source zones of such disastrous earthquakes would be an important contribution to seismic hazard assessment. In this study, we have worked out spatio-temporal clustering of earthquakes (Mb ?? 4.5; 1964?C2006) in the Himalayas. ??Point density?? spatial statistics has helped in detecting 22 spatial seismicity clusters. Earthquake catalog is then treated with a moving time-distance window technique (inter-event time 35 days and distance 100 ± 20 km) to bring out temporal clusters by recognizing several foreshock-main shock-aftershock (FMA) sequences. A total of 53 such temporal sequences identified in the process are confined within the 22 spatial clusters. Though each of these spatio-temporal clusters deserves in-depth analysis, we short-listed only eight such clusters that are dissected by active tectonic discontinuities like MBT/MCT for detail study. Spatio-temporal clusters have been used to constrain the potential source zones. These eight well-defined spatio-temporal clusters demonstrate recurrent moderate to large earthquakes. We assumed that the length of these clusters are indicating the possible maximum rupture lengths and thus empirically estimated the maximum possible magnitudes of eight clusters that can be generated from them (from west to east) as 8.0, 8.3, 8.2, 8.3, 8.2, 8.4, 8.0 and 7.7. Based on comparative study of the eight cluster zones contemplating with their temporal recurrences, historical seismic records, presence of intersecting faults and estimated magnitudes, we have guessed the possibility that Kangra, East Nepal, Garhwal and Kumaun?CWest Nepal clusters, in decreasing order of earthquake threat, are potential source zones for large earthquakes (??7.7 M) in future.     

对我国地震地质特点的一些初步认识

我国的地震地质工作是随着社会主义建设的进展而提出来的,在毛主席“备战,备荒,为人民”的号召下,自无产阶级文化大革命以来得到了更大的发展。本文是在整理中国地震地质资料的基础上写成的。由于地震地质的许多问题尚处于探索阶段,因此我们只是提出一些粗浅的看法,以便和从事这一工作的同志们共同讨论。     

Probabilities of earthquake occurrences in Mainland Southeast Asia

The frequency–magnitude distributions of earthquakes are used in this study to estimate the earthquake hazard parameters for individual earthquake source zones within the Mainland Southeast Asia. For this purpose, 13 earthquake source zones are newly defined based on the most recent geological, tectonic, and seismicity data. A homogeneous and complete seismicity database covering the period from 1964 to 2010 is prepared for this region and then used for the estimation of the constants, a and b, of the frequency–magnitude distributions. These constants are then applied to evaluate the most probable largest magnitude, the mean return period, and the probability of earthquake of different magnitudes in different time spans. The results clearly show that zones A, B, and E have the high probability for the earthquake occurrence comparing with the other seismic zones. All seismic source zones have 100 % probability that the earthquake with magnitude ≤6.0 generates in the next 25 years. For the Sagaing Fault Zone (zones C), the next Mw 7.2–7.5 earthquake may generate in this zone within the next two decades and should be aware of the prospective Mw 8.0 earthquake. Meanwhile, in Sumatra-Andaman Interplate (zone A), an earthquake with a magnitude of Mw 9.0 can possibly occur in every 50 years. Since an earthquake of magnitude Mw 9.0 was recorded in this region in 2004, there is a possibility of another Mw 9.0 earthquake within the next 50 years.     

Universal precursor seismicity pattern before locked-segment rupture and evolutionary rule for landmark earthquakes

Despite extensive investigations, no precursor patterns for reliably predicting major earthquakes have thus far been identified. Seismogenic locked segments that can accumulate adequate strain energy to cause major earthquakes are highly heterogeneous and low brittle. The progressive cracking of the locked segments with these properties can produce an interesting seismic phenomenon: a landmark earthquake and a sequence of smaller subsequent earthquakes (pre-shocks) always arise prior to another landmark earthquake within a well-defined seismic zone and its current seismic period. Applying a mechanical model, magnitude constraint conditions, and case study data of 62 worldwide seismic zones, we show that two adjacent landmark earthquakes reliably occur at the volume-expansion point and peak-stress point (rupture) of a locked segment; thus, the former is an identified precursor for the latter. Such a precursor seismicity pattern before the locked-segment rupture has definite physical meanings, and it is universal regardless of the focal depth. Because the evolution of landmark earthquakes follows a deterministic rule described by the model, they are predictable. The results of this study lay a firm physical foundation for reliably predicting the occurrence of future landmark earthquakes in a seismic zone and can greatly improve our understanding of earthquake generation mechanism.